COAL DEPYRITIZATION BY THE THERMOPHILIC ARCHAEON METALLOSPHAERA-SEDULA

The kinetics of pyrite oxidation by Metallosphaera sedula were investi gated with mineral pyrite and two coals with moderate (Pittsburgh no. 8) and high (New Brunswick, Canada) pyritic sulfur content. M. sedula oxidized mineral pyrite at a greater rate than did another thermophile , Acidianus brierleyi, or a mesophile, Thiobacillus ferrooxidans. Maxi mum rates of coal depyritization were also greater with M. sedula, alt hough the magnitude of biological stimulation above abiotic rates was notably less than with mineral pyrite. Coal depyritization appears to be limited by the oxidation of pyrite with ferric ions and not by the rate of biotic oxidation of ferrous iron, as evidenced by the maintena nce of a high ratio of ferric to ferrous iron in solution by M. sedula . Significant precipitation of hydronium jarosite at elevated temperat ure occurred only with New Brunswick coal.